Recently, in consideration of environmental issues, vehicles using electric motors as driving power sources such as electric vehicles, hybrid vehicles and fuel cell electric vehicles have been attracting attention. Such a vehicle is provided with a rechargeable electric storage unit for supplying electric power to an electric motor and for converting kinetic energy to electric energy at the time of regenerative braking and for storing the same.
Use of an electric vehicle with such an electric storage unit as an electric power source of a house or the like has been proposed. By way of example, Japanese Patent Laying-Open No. 2001-008380 discloses a power management system that allows transmission of electric power between a house and a battery mounted on an electric vehicle. In the power management system, amount of electric power supplied from the electric vehicle to the house is managed in accordance with the power supplied from the mains to loads in the house.
Electric vehicles such as represented by hybrid vehicles are rapidly becoming common due in part to lower costs enabled by technical innovation. Along with the widespread use of electric vehicles, it is fully expected that a large number of households own a plurality of electric vehicles.
The power management system disclosed in Japanese Patent Laying-Open No. 2001-008380 considers only a configuration in which one electric vehicle is electrically connected to one house, and not a configuration in which a plurality of electric vehicles are electrically connected to one house.
As disclosed in Japanese Patent Laying-Open No. 2001-008380, the electric power supplied from an electric vehicle to the house is not DC power but AC power, so as to enable power supply to loads in the house in coordination with mains power (AC power). Generally, in order to implement coordination among a plurality of AC power sources, voltages, frequencies and phases must be matched with each other. Therefore, it has been difficult to realize the configuration in which a plurality of electric vehicles are electrically connected to one house.